High frequency inductance coil



y 1939. w. D. LOUGHLIN 2,158,613

HIGH FREQUENCY INDUGTANCE COIL Filed Nov. :5, 1936 2 sheets-Sheet 1 I I I J I g L I I 1 J I I J'" l l I y 1939. w. 0. LOUGHLIN HIGH FREQUENCY INDUCTANCE COIL Filed Nov. a, 1956 2 Sheets-Sheet 2 Patented May 16, 1939 g UNITED STATES PATENT OFFICE HIGH FREQUENCY OOIL William D. Loughlin, Mountain Inkesgfl. J., assignor, by mesne alignments, to Ferrocart Corporation of America, New York, N. Y., a corporation of Delaware Application November 3, 1938, Serial No. 109,010

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This invention relates to high frequency inductance coils for use in radio receivers, and more particularly to low loss iron cored coils.

It has been proposed to wind exceedingly small 5 multilayer coils and to enclose the same within small cylindrical shells formed of minute insulated particles of ferromagnetic material, the entire assembly for the broadcast range having a diameter of the order of not more than one inch and a length of the order of not more -half than three-eighths of an inch. Completely enclosed miniature coils of this type are contemplated by this invention.

An object of the invention is to provide improved physical constructions and circuit arrangements for high frequency inductances of the small size and completely or substantially completely enclosed in magnetic material. object is to provide iron cored inductance An coils of the completely enclosed type and mountings and shielding apparatus for the same.

An obsubstantially completely enclosed in mag netic material. Further, objects are to provide transformers of the type stated which include members adjustable to vary the coupling between the windings.

These and other objects and advantages f the invention will be apparent from the following specification when taken with the accompanying drawings in which:

Figs. 1,2 and 3 are enlarged sectional views through embodiments of the invention;

Fig. 4 is a longitudinal sectional view thr a shielded coil assembly;

ough

Fig. 5 is a similar sectional view through a shielded transformer assembly;

Fig. 6 is a longitudinal sectional view thr ough a transformer which includes an adjustable member for trimming one inductance;

Figs. 7 and 8 are, respectively, a plan view and a section on line 8-8 of Fig. '7, of a coil and core mounting, a portion of the core being adius to trim the inductance;

table Fig. 9 is a plan view of a modified form of adjustable core mounting;

Fig. 10 is a sectional view of another form of coil and adjustable core assembly;

Figs. 11 and 12, are, respectively, fragmentary plan and side elevations of another coil and mounting;

Figs. 13 and 14 are schematic views with the core and coil elements shown in section. illustrating different circuit arrangements for inductance coil assemblies embodying the invention;

Fig. 15 is a, side elevation of a radio frequency transformer, the shield can being broken away;

Figs. 16 and 1'1 are views, as seen from oppoute sides, of the transformer assembly removed from the shield can;

Fig. 18 is a side elevation; with parts in section. of another transformer assembly; and

Fig. 19 is a plan view of. the same.

As shown in Fig. 1, the core of magnetic material takes the form of a small cylindrical cup or shell i having a central core 2 rising from the bottom wall of the shell, and a cover plate or disk 3 which snugly fits the top surfaces of the cylindrical wall and the central core. Magnetic core material for use with high frequency coils is now manufactured commercially and may comprise minute particles of iron or other magnetic material which are held together and electrically insulated from each other by a binder. The core assemblies of Figs. 2 and 3 have the same crosssection as that shown in Fig. l, but the central core 2 is integral with the cap 3', and the shelll has a central aperture in its end wall for snugly receiving the end of the core 2. Small openings 4 may be made in the shell I for passing the terminals of the coil to the exterior of the core, or. the openings 4 may be formed in the cap I.

It is to be noted that Figs. 1-3 are enlarged views of cores appropriate for use at broadcast and higher frequencies, and that the diameter of the shell may be as low as about it inch, and the overall length of the shell and cap as low as about inch. The volume of such cores is of the order of .033 cubic inch or less than 1 cubic centimeter, and the weight is of the order of less than 4 grams. The coils are preferably of the type known as universal windings, with the adjacent turns of each layer spaced from each other. Each coil is supported on and spaced from the central core by insulating material, such as waxed paper. The coils of Figs. 1-3 are designed for different uses and the coils are identified by reference numerals 5a, 5b, 5c, respectively, and the corresponding insulating bushings by numerals 8a, 6b and 6c. The cores for the three coils may be, and preferably are, of identical size.

The coil 5a of Fig. 1 is designed for condensertuning over the broadcast band, coil 5b of Fig. 2 is designed for use at an intermediate frequency of 450 kiiocycles, and core 0 of Fig. 8 is designed for condenser-tuning over the band of from 1500 kilocycles to 4500 kilocycles. Designating the axial length of the coil as A, and the internal and external diameters as D and D, respectively, the following data is indicative of the appropriate design and characteristics of the three types of coils. The advantages of the coils as high frequency inductances is shown by the high values'of Q or where L is the inductance and R the resistance of the coil.

Callba- 550-1500 k. 0....-- 460 k. c

14001:. c.-l50... 1000 k. c.-l 760 k. c.-Zl0.... 550k. c.-200..-.

In general, the design requirements are that, with increasing frequency, the separate strands of the Litzendraht wire should be of smaller size, with thicker insulation and greater spacing between adjacent turns. The spacing of the coil from the core should also increase with frequency, but this requirement may be satisfied with cores of a single size since the coil size decreases with frequency. It will be noted that the wall of the insulated tube 60 on which coil 50 is wound is of substantially greater thickness than the wall of tube 611 of coil is.

The coils may be securely fixed in place by a filling of melted wax I, as shown in Fig. 3, and the parts of the core may be locked in place by applying a drop of wax 8 over the end of core 2 and the adjacent portion of shell I. Inductances may be manufactured with high uniformity when .the core form of Figs. 2 and 3 is used since the coil may be accurately positioned on the central core section and the snug fit of the cores 2' in the openings in shells I thus locates the core and coil elements in definitely predetermined positions. The coils may be wound in situ on tubes 6 placed on the cores 2' but must be prewound for insertion in the cup I of the core of Fig. 1.

The small leakage field of the enclosed coils materially reduces the size of the cans commonly used to shield the inductances or, if desired, the cans may be of the usual large sizes but cheaper material, such as tinned iron. As shown in Fig. 4, the coil 5 and its core may be secured at a desired position within an insulating tube 9 by wax Ill, and the tube may be fixed to a base II by a bolt I2 that extends through a wooden dowel I3 that fits snugly or is sealed by wax to the tube. An aluminum or copper shield I4 fits over the tube and base, and is secured in place by bent tongues I5. When the core shell 3, or 3, is approximately one-half inch in diameter, the diameter of the shield can I4 may be as low as about three-quarters of an inch without introducing losses .that materially affect the electrical characteristics of the inductance.

The usual trimming condensers may be replaced by small fixed condensers by mounting a closed conductive band or ring I6 on the tube 9. The coils are wound with a few extra turns and are then trimmed to bring the inductance to the exact required value by adiusting the ring I 3 along the tube.

The general arrangement of Fig. 4 is applicable in the case of coupled coils. A primary winding I1 may be arranged outside the tube 3, Fig. 5, when it is not essential that the primary be of low resistance, or the coils may be enclosed in separate magnetic cores N, Fig. 6, when a low resistance primary isdesired. As shown in Fig. 5, a conductive plate I 3 may be adjusted within the tube 3 to trim the inner coil, or, as in Fig. 6, the cap 3 may be used as an inductance trimmer. The cap 3 is secured to the insulated head I8 on a bolt I3 that is threaded in the base 20. Rotation of the head is prevented by a pin 2|, and aspi ing 22 liftsthe head and core cap when the nut is backed off of bolt I3.

Trimming may also be effected by moving the cap 3 in a plane transverse to the axis of the shell I. As shown in Fig. 7, the shell I may be supported by and with its upper edge flush with the surface of an insulating base 23, while the cap 3 is mounted in a recess in the insulating plate 24 that is pivotally mounted on the base 23. The end 25 of plate 24 is cut as gear teeth which mesh with an adjusting screw 23 that is mounted in a bracket 21. Terminals 23 for the coil 5 may be riveted to the base 23.

As shown in Fig. 9, the pivoted plate 24' which carries the cap 3 of a coil-core assembly may be urged in one direction by a spring 29 and forced in the opposite direction by a bolt 30.

As shown in Fig. 10, the insulating plates 3|, 32 which carry the shell I and cap 3 of a corecoil assembly are pressed toward each other by a spring 33, and the cap end of plate 32 may be rocked away from the base 3| by a bolt 34. One or more pins 35 on plate 32 engage recesses in the plate 3| to form a hinge joint for the pivoted plate. The bolt 33 secures the spring 33 to the base plate and is of such length as to found, however, that substantially no losses are introduced when the coil-core assemblies are mounted upon metallic plates of good electrical conductivity, such as plates of copper, aluminum or a zinc alloy known commercially under the trade mark Eraydo. The shell I of magnetic material must be insulated from the metallic plate 31, for example by a short tube or winding 3' of paper, oiled silk or the like. The effect of the metal adjacent the core 5 is reduced when, as shown in Figs. 11 and 12, the metal does not completely enclose the magnetic shell. The end plate 31 is bifurcated to form a yoke for receiving the tube 9 with a close sliding fit, or the assembly may be secured in place by wax or by compressing the arms of the plate upon the insulating tube. The cap 3 is omitted from Fig. but it is to be understood that the core 5 must be substantially completely enclosed in magnetic material to reduce to a minimum that portion of the magnetic field which cuts the metal mounting plate. Mounting plates of metal may be of smaller size than plates of insulating material and where space requirements are rigid, are to be preferred to the insulating material mountings.

Although the leakage field of the coil is repletely enclosed within a shell of magnetic mafrequency range.

terial, I have found that, when the coil I has a high Q, i. e., of the order of and upward, it is entirely practical to obtain more than critical coupling between the coil Ii and a coil ll exterior to the shell I. The high Q value for coil 5 may beobtained, as described above, by universal windings of Litzendraht wlre appropriately designed for the required frequency or The coil Il may be the primary winding of a transformer coupling between tubes 39, 40, see Fig. 13,- or the coils may be serially connected, in the same manner as coils 5, 38' of Fig. 14, as sections of a double frequency range inductance. Winding 38' is within the core structure but it is to be understood that either the external or the internal type of coupled winding may be used in the circuits of Figs. 13 and 14. For a double range system, both windings are used for the lower frequency and winding 38 or 38' is shunted .by a switch 4! when operating in the higher range.

The coil-core assemblies are well adapted for use in intermediate frequency transformers, and

typical constructions for the condenser trimmed types of transformers are shown in Figs. 15 to 9. The base 42 is formed'of insulating material, such as a molded plastic or ceramic material, and has ribs 43 at one side to engage the shield can 44 and leave space for the trimming condensers 45 between the base and the can. Screws 4. are threaded into the ribs 41 to secure the base within the shield can. Pillars 41 extend from the base and have bores within which the shells I of the coil assemblies are mounted. The spacing of the adjacent surfaces of the pillars is such that a desired degree of overcoupling for a band pass efl'ect is obtained when the magnetic shells are flush with these faces of the pillars. For convenience in trimming the coils, the base '42 is slotted, as at ll, and the shield can has an alined opening through which a strip of metal 49, such as copper, may be introduced to reduce the coupling to less than critical. Terminals I are mounted at the inner face of the base 4! for establishing circuit connections to the transformer, the terminals being connected in the usual manner to the coils and the trimmer condensers.

The transformer shown in Figs. 18 and 19 includes a base I, asidewall II and a transversewall II onwhichoneshell I and its mclosed coll are mounted. A pivoted wall or plate ll carries the second coil assembly and. u shown, the plate maybepivotallymmmtcdtopermit adjustment of the coupling between the coils. Plate I4 is urged towards the fixed wall H by a spring I! and may be forced in the opposite direction by a bolt 56. Trimmer condensers may be mounted on the side wall 52 or the coils may be inductance trimmed by the methods described above.

It is particularly to be noted that the various embodiments of the invention herein described satisfy the practical design requirement of high efliciency at radio frequencies. The high values of Q which are obtained with universal windings of low copper content and spaced, as required for different frequency ranges, from the enclosing magnetic material permit the coupling of an external winding to a completelyenclosed coil and the coupling, with rnore than critical coupling, of two coils which are each completely enclosed in shells of magnetic material. Substantial economies in the size of radio receivers are therefore possible and, in this connection, attention is again directed to the fact that, except for Figs. 18 and 19, the several views of the drawings show the various parts in more than actual size.

1 I claim:

1. A transformer for use at high frequencies, comprising a shield can, an insulating base within said can and supported on one side wall thereof, apertured pillars projecting from said base, and an inductance assembly comprising a coil and a magnetic core mounted in the aperture of each pillar, said base and said side wall having openings in line with each other and with the space between said apertured pillars, whereby a decoupling metal strip may be inserted between said coil assemblies when the coils are to be adjusted individually to resonance.

2. A transformer comprising a shield can, a base of insulating material within said can and having ribs projecting from one face thereof to engage a side wall of the can, means entering said ribs to secure the base to the can, spaced pillars projecting from the other face of the base, said pillars having bores extending therethrough, a magnetic core in each bore and carrying a coil, and adjustable trimmer condenser connected across each coil, and means supporting said condensers on said base at the face thereof adjacent said side wall of the shield can,

' said side wall having openings therethroughprovidingaccess to the condenser for adjustment 

